Photon induced isomerization in the first excited state of the 7-azaindole-(H2O)3 cluster

A picosecond pump and probe experiment has been applied to study the excited state dynamics of 7-azaindole-water 1?∶?2 and 1?∶?3 clusters [7AI(H(2)O)(2,3)] in the gas phase. The vibrational-mode selective Excited-State-Triple-Proton Transfer (ESTPT) in 7AI(H(2)O)(2) proposed from the frequency-resolved study has been confirmed by picosecond decays. The decay times for the vibronic states involving the ESTPT promoting mode σ(1) (850-1000 ps) are much shorter than those for the other vibronic states (2100-4600 ps). In the (1 + 1) REMPI spectrum of 7AI(H(2)O)(3) measured by nanosecond laser pulses, the vibronic bands with an energy higher than 200 cm(-1) above the origin of the S(1) state become very weak. In contrast, the vibronic bands in the same region emerge in the (1 + 1') REMPI spectrum of 7AI(H(2)O)(3) with picosecond pulses. The decay times drastically decrease when increasing the vibrational energy above 200 cm(-1). Ab initio calculations show that a second stable "cyclic-nonplanar isomer" exists in addition to a "bridged-planar isomer", and that an isomerization from a bridged-planar isomer to a cyclic-nonplanar isomer is most probably responsible for the short lifetimes of the vibronic states of 7AI(H(2)O)(3).     

High-throughput turbidimetric screening for heparin-neutralizing agents and low-molecular-weight heparin mimetics

Safer heparin-neutralizing agents are currently required to replace protamine, the use of which causes adverse effects such as anaphylaxia. Low-molecular-weight (LMW) heparin mimetics that potentiate antithrombin III (AT) action are also valuable as anti-thrombotics. This paper describes a high-throughput assay for both heparin-neutralizing agents and LMW heparin mimetics without the use of blood preparations. The assay is based on turbidimetric measurement of a solution of collagen, heparin, and a test compound. Native collagen molecules spontaneously form insoluble fibrils when transferred to a physiological buffer, and this process is inhibited by heparin. In the presence of a heparin-neutralizing agent or an LMW heparin mimetic, the inhibitory effect of heparin is canceled and turbidity increase is retrieved. We demonstrated that this assay is effective in detecting potential agents with high reliability (Z' factor=0.9). The screening of a chemical library (34400 compounds) was further performed in a 384-well format, and led to the identification of a novel heparin-neutralizing agent. Since this assay protocol is feasible for an automated high-throughput screening (HTS) system, it could enhance the lead seeking process for drugs related to heparin/heparan sulfate (HS) functions.     

A further study on the combined use of internal standard and isotope-labeled derivatization reagent for expansion of linear dynamic ranges in liquid chromatography-electrospray mass spectrometry

The combined use of a so-called internal standard and the isotope-labeled derivatization reagent for the quantification of analytes for liquid chromatography-mass spectrometry (LC/MS) was further studied. The sample solution (containing the analytes and an internal standard) was derivatized with the light form of the derivatization reagent, 7-(N,N-dimethylaminosulfonyl)-4-(aminoethyl)piperazino-2,1,3-benzoxadiazole (DBD-PZ-NH(2)) or 7-(N,N-dimethylaminosulfonyl)-4-piperazino-2,1,3-benzoxadiazole (DBD-PZ). A standard solution of the analytes (containing an internal standard) was derivatized with the isotope (d(6))-labeled derivatization reagent, DBD-PZ-NH(2) (D) or DBD-PZ (D), and served as the isotope-labeled internal standards. The peak heights of the targeted analytes derivatives in the sample solution were corrected using those of the internal standard and the heavy form derivatives of the standards, and the calibration curves were constructed. The curve bending of the calibration curves caused by the ion suppression at the ion source was suppressed and the linear dynamic ranges of the calibration curves were expanded. The derivatives of DBD-PZ-NH(2) were about 10 times more sensitively detected than those of DBD-PZ derivatives and, therefore, DBD-PZ-NH(2) might be suitable for sensitive detection.     

Kinetics for the gas‐phase reactions of OH radicals with the hydrofluoroethers CH2FCF2OCHF2, CHF2CF2OCH2CF3, CF3CHFCF2OCH2CF3, and CF3CHFCF2OCH2CF2CHF2 at 268–308 K

Rate constants were determined for the reactions of OH radicals with the hydrofluoroethers (HFEs) CH₂FCF₂OCHF₂(k₁), CHF₂CF₂OCH₂CF₃ (k₂), CF₃CHFCF₂OCH₂CF₃(k₃), and CF₃CHFCF₂OCH₂CF₂CHF₂(k₄) by using a relative rate method. OH radicals were prepared by photolysis of ozone at UV wavelengths (>260 nm) in 100 Torr of a HFE–reference–H₂O–O₃–O₂–He gas mixture in a 1‐m³ temperature‐controlled chamber. By using CH₄, CH₃CCl₃, CHF₂Cl, and CF₃CF₂CF₂OCH₃ as the reference compounds, reaction rate constants of OH radicals of k₁ = (1.68) × 10^?12 exp[(?1710 ± 140)/T], k₂ = (1.36) × 10^?12 exp[(?1470 ± 90)/T], k₃ = (1.67) × 10^?12 exp[(?1560 ± 140)/T], and k₄ = (2.39) × 10^?12 exp[(?1560 ± 110)/T] cm³ molecule^?1 s^?1 were obtained at 268–308 K. The errors reported are ± 2 SD, and represent precision only. We estimate that the potential systematic errors associated with uncertainties in the reference rate constants add a further 10% uncertainty to the values of k₁–k₄. The results are discussed in relation to the predictions of Atkinson's structure–activity relationship model. The dominant tropospheric loss process for the HFEs studied here is considered to be by the reaction with the OH radicals, with atmospheric lifetimes of 11.5, 5.9, 6.7, and 4.7 years calculated for CH₂FCF₂OCHF₂, CHF₂CF₂OCH₂CF₃, CF₃CHFCF₂OCH₂CF₃, and CF₃CHFCF₂OCH₂CF₂CHF₂, respectively, by scaling from the lifetime of CH₃CCl₃. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 239–245, 2003     

Direct ethoxycarbonyldifluoromethylation of aromatic compounds using Fenton reagent

Direct ethoxycarbonyldifluoromethylation of aromatic compounds by BrCF₂CO₂Et was investigated using Fenton reagent in dimethylsulfoxide. Various five-membered hetero-aromatic compounds, benzene derivatives and uracil having ethoxycarbonyldifluoromethyl group were obtained catalytically with the combination of ferrocene and H₂O₂ at room temperature. The ethoxycarbonyldifluoromethylation occurred at the position predicted by the trend of the electrophilic substitution of aromatic compounds. When para-substituted aniline derivatives were used as a substrate, the one-pot synthesis of 3,3-difluoro-2,3-dihydroindole-2-one derivatives was achieved through the ethoxycarbonyldifluoromethylation at the ortho-position to the amino group and the consecutive intramolecular amidation of the amino group and the adjacent ethoxycarbonyldifluoromethyl group.     

Palladium metal-catalyzed cross-coupling of aryl iodides with arylmagnesium bromides. Synthesis of fluorobiphenyls

Palladium metal functions as catalyst in the coupling of iodobenzene with phenylmagnesium bromide. For practical purposes, palladium(II) chloride was used instead, since it is converted to palladium metal during the course of the reaction. A high catalytic effect of palladium(II) chloride at low concentrations (saturated solutions in tetrahydrofuran, < 0.0001 molar equiv.) was exhibited in cross-couplings yielding several fluorobiphenyls.